The dust-rich, gas-depleted protosolar disk as the birthplace of chondrules

Abstract

Chondrules are the primary components of primitive meteorites known as chondrites, and understanding their formation and accumulation is essential for elucidating the history of planet formation in the Solar System. Although a variety of chondrule formation mechanisms have been proposed, it remains challenging to satisfy the key constraints on chondrule abundance, formation timing, and mineralogical and chemical characteristics within a single model. In particular, the planetesimal bow-shock model, once considered one of the leading candidates, now faces a fundamental difficulty: Jupiter's formation likely depleted gas in the protosolar disk, potentially lowering the gas density below that required for efficient chondrule formation by planetesimal bow shocks. Here we propose an alternative mechanism that can occur in a gas-depleted environment: heavy bombardment of eccentric planetesimals by debris dust. After Jupiter formed in the protosolar disk, the region interior to its orbit became gas-depleted, leading to the formation of a geometrically thin debris-dust layer. When planetesimals enter the dust layer at high speed, large quantities of molten silicate droplets are produced. These droplets cool and solidify into chondrules and are reincorporated into the dust layer. Using analytical calculations, we find that our model can potentially explain the abundance, formation timing, and mineralogical and chemical characteristics of chondrules. This study links the formation of Jupiter and the accompanying evolution of the protosolar disk to the origin of terrestrial planets, asteroids, and meteorites, thereby offering a new framework for the formation of the Solar System.